The present invention relates to a radiation sensitive material and a process for forming a pattern using the same.
Recently, semiconductor integrated circuits have become more integrated and LSIs and VLSIs are practically available. Accompanying such integration, circuit patterns have become smaller in size, approaching submicron dimensions and even smaller. Formation of a pattern in a submicron dimension essentially requires lithography. In lithography a thin film resist is deposited on to a substrate to be processed, and is selectively exposed and developed to form a resist pattern. With this resist pattern as a mask, dry etching is conducted and then the resist is removed to obtain a required pattern. As an exposure source for lithography, ultraviolet radiation was originally used, but as circuit patterns approach submicron sizes, far ultraviolet radiation (e.g. electron beams, X rays, etc.) with short wavelengths, are used as exposure sources.
Especially for lithography using excimer lasers (248-nm wavelength KrF laser and 193-nm wavelength ArF laser), resist materials having high resolution, high sensitivity and good dry-etching resistance are required.
Many conventionally developed resists are based on phenol resin and novolak resin. These materials have aromatic rings and good dry etching resistance, but they have poor transparency at KrF wavelength and are totally opaque at ArF wavelength. Consequently they can not provide patterns sufficiently precise in submicron dimensions.
On the other hand, as a transparent resist for excimer beams, t-butyl methacrylate polymer is proposed, but this resist lacks dry etching resistance.
As a countermeasure to this, the inventors have proposed a chemical amplification type resist using alicyclic groups as a resist having dry etching resistance comparable with that of aromatic compounds and are transparent at KrF and ArF wavelength. Here alicyclic groups are adamantane, norbornane, perhydroantracene, cyclohexane, tricyclo[5.2.1.02,6]decane etc., and adamantyl groups are suitable (see Japanese Patent Laid-Open Publication No. 39665/1992).
But the chemical amplification type resist of alicyclic copolymer increases hydrophobicity and rigidity of the alicyclic group, which gives dry etching resistance, increases its composition ratio.
At a composition ratio which gives dry etching resistance comparable to that of phenol resin-based and novolak resin-based resists, e.g., above 50 mol % of alicyclic unit, because of high hydrophobicity and rigidity of the resists, diffusion of protonic acid as a catalyst is hindered, which results in lower amplification, smaller amounts of carboxylic acid being generated, and lower solubility to a developer of an alkaline aqueous solution.
Furthermore, these resists lack adhesiveness, and, in addition, their resist films are rigid because of inclusion of alicyclic groups. As a result, strain caused to the resist films become larger, and the resist films have a greater tendency to peel off. Accordingly stable pattern characteristics cannot be obtained. This is also a problem.